Preparation of heat insulating materials of foamed plastics using blowing agents which provide the material with a gas-filled cell structure is well known in the art. In foamed plastics for insulating purposes the solid phase is often made of polyurethane and the gas phase, that is the blowing agent is chlorofluorocarbons (CFC substances), for instance trichlorofluoromethane (CFC 11). Because of their low thermal conductivity, CFC substances provide foamed plastics suitable for heat insulation. In addition to this, they have a suitably low boiling point, which presents an advantage to the method of preparation, they are chemically inactive to the solid plastic materials of the foamed material and are stable in their environment of use. The use of said CFC substances is however encumbered with the drawback that they are damaging to the environment. In recent years, a potential problem has come to light in that when exposed to ultra-violet rays the otherwise stable CFC substances are decomposed in the upper atmosphere, whereby halogens are released which decompose the ozone layer. Therefore, there is a growing need for alternative insulating materials which do not involve harmfull halogen-containing blowing agents both in order to meet the wishes of environment-conscious consumers and to forestall problems in connection with legal restrictions, prohibitions or increased purification requirements to be expected in the future.
To replace said substances, it has been suggested to use similar substances which in addition to halogen atom(s) contain at least one hydrogen atom, for instance HCFC substances. Said substances distinguish themselves from the traditional CFC substances in that they are less stable and therefore only a smaller quantity is expected to reach the upper atmosphere. The decomposition products of said materials may however be expected to cause other environmental problems, for instance hydrochloric acid rain and hydrofluoric acid rain. Furthermore, it is expected that the preparation of HCFC substances will be substantially more costly than the preparation of CFC substances.
As the cells of the heat insulating foamed plastic materials make up the major portion of the volume, the heat conduction taking place through the gas present in the cavity of the cells contributes considerably to the total thermal conductivity of the insulating material, said contribution conventionally comprising about half of the heat conduction in the case where the cells are filled with CFC 11. Therefore, when preparing a foamed plastic material with a good heat insulating capacity, it is decisive that the gas present in the cells per se have a low thermal conductivity.